The natural philosophy of plant form:: Cellular autoreproduction as a component of a structural explanation of plant form

A map-L-system is described which simulates the development of the two-dimensional patterns of cell walls displayed at the surfaces of shoot apices of Psilotum nudum. The simulation of these cellular patterns commences with the division of a triangular cell and continues until a complete set of ten different cells, including new triangular cells, is formed amongst the descendants of each merophyte. The triangular cells generated by means of this division pathway. P1, are, in their three-dimensional aspect, four-sided apical cells. In the plant, they have the potentiality to support the development of a shoot apex. The generation of new triangular cells by pathway PI therefore seems to be a precondition for the branching of the shoot. Observed variations upon the cellular pattern developed by pathway P1 have also been analysed. Two of these variant pathways, P2 and P3, suggest the types of controls which are required to bring about all three (P1-P3) patterns of cells. These controls may involve the participation of the plant cytoskeleton and may also require an influence from the apical cell itself, The triangular shoot apical cells of Psilotum are autoreproductive cells: that is, at each division, one of the daughters is a new triangular cell, the other daughter has some other shape, This example of triangular cell autoreproduction and self-maintenance and its relation to organogenesis is discussed in light of the views on reproduction and self-maintenance expressed by Agnes Arber (1950) in her book The natural philosophy of plant form (Cambridge: Cambridge University Press). (C) 2001 Annals of Botany Company.